Role of the hepatic xanthine oxidase in thyroid dysfunction: effect of thyroid hormones in oxidative stress in rat liver

Deneysel hipertiroidide fiziksel ve vital bulguların ve karnozinin etkisinin değerlendirilmesi

Purpose: This study aims to investigate the effects of experimental hyperthyroidism and carnosine which is known to have antioxidant properties on physical and vital findings in rats, and to determine the relationship between these parameters and free T3 (FT3) levels. Materials and Methods: Rats were analyzed in 7 groups (each containing 12 animals); control (CONT), hyperthyroidism-1 (T:10-day L-thyroxine (L-T4) administration), hyperthyroidism-2 (T-T: 20-day L-T4 administration), Carnosine (10 day carnosine administration), Hyperthyroidism-1 + Carnosine (T-C), Hyperthyroidism-2 + Carnosine (T-TC), and Carnosine + Hyperthyroidism-1 (C-T). In order to create a hyperthyroidism model, L-thyroxine (L-T4) doses of 300 µg/kg rat weight/day and carnosine doses of 300 µg/kg rat weight/ day were intraperitoneally (ip) administered to the rats. Results: After 10 and 20 days of thyroxine administration, FT3 levels (T:3.640.51pg/mL, T-T: 4.060.91pg/mL) and body temperature (T:37.10.3oC, T-T: 37.60.3oC), significantly increased while body weight decreased (T:240.722.0g, T-T:263.028.7g). Carnosine administration only prevented the increase of FT3 levels, but had no effect on other parameters. Conclusion: The increased FT3 levels observed with L-T4 administration were consistent with the physical and vital findings, but carnosine administration did not reflect the expected effects on the physical findings observed in the hyperthyroid condition.

Functional State of Rat Heart Mitochondria in Experimental Hyperthyroidism

In this work, the effect of thyroxine on energy and oxidative metabolism in the mitochondria of the rat heart was studied. Hyperthyroidism was observed in experimental animals after chronic administration of T₄, which was accompanied by an increase in serum concentrations of free triiodothyronine (T₃) and thyroxine (T₄) by 1.8 and 3.4 times, respectively. The hyperthyroid rats (HR) had hypertrophy of the heart. In HR, there was a change in the oxygen consumption in the mitochondria of the heart, especially when using palmitoylcarnitine. The assay of respiratory chain enzymes revealed that the activities of complexes I, I + III, III, IV increased, whereas the activities of complexes II, II + III decreased in heart mitochondria of the experimental animals. It was shown that the level of respiratory complexes of the electron transport chain in hyperthyroid rats increased, except for complex V, the quantity of which was reduced. The development of oxidative stress in HR was observed: an increase in the hydrogen peroxide production rate, increase in lipid peroxidation and reduced glutathione. The activity of superoxide dismutase in the heart of HR was higher than in the control. At the same time, the activity of glutathione peroxidase decreased. The obtained data indicate that increased concentrations of thyroid hormones lead to changes in energy metabolism and the development of oxidative stress in the heart of rats, which in turn contributes to heart dysfunction.

Vitamin D improves oxidative stress and histopathological damage in rat ovaries caused by hyperthyroidism

OBJECTIVE

The aim of this study is to investigate the histopathological and biochemical efficacy of vitamin D on oxidative damage and fibrosis in rat ovaries induced by experimental hyperthyroidism.

METHODS

This study is a comparative, prospective experimental rat study. Sprague-Dawley female rats were divided into four groups. Only distilled water was given to the rats in group 1 for 25 days. In group 2, 100 μg/day L-thyroxine was given to rats for 25 days. In Group 3, 100 μg/day L-thyroxine and 200 IU/day vitamin D were given to rats for 25 days. In group 4, only 200 IU/day vitamin D was administered for 25 days.

RESULTS

This study is the first to demonstrate the protective effect of vitamin D against ovarian damage caused by experimental hyperthyroidism. Hyperthyroidism caused fibrotic degenerative changes in the ovaries and an increase in the fibrillin 1 score. It caused serum follicle-stimulating hormone (FSH) levels to increase and serum E2 levels to decrease. In addition, malondialdehyde (MDA) and total oxidant status (TOS) levels increased in rats with hyperthyroidism. Vitamin D decreased MDA and TOS values and increased total antioxidant status (TAS) values in rats with hyperthyroidism. It also increased TSH values by causing a decrease in TT3 and TT4 values. It decreased fibrosis, follicle degeneration, stromal degeneration, and fibrillin 1 score in ovarian tissue.

CONCLUSION

Vitamin D has positive histopathological and biochemical effects on the oxidative stress and follicle damage caused by hyperthyroidism in ovarian tissue. Human studies with larger case populations should be conducted to evaluate the effects and clinical applications of vitamin D.

Energy metabolism and oxidative status of rat liver mitochondria in conditions of experimentally induced hyperthyroidism

The aim of the present work was to investigate the energy metabolism and antioxidant status of rat liver mitochondria using a model of hyperthyroidism. In experimental animals, the level of triiodothyronine and thyroxine was increased 3- and 4-fold, respectively, in comparison with that in the control group, indicating the development of hyperthyroidism in these animals. Oxygen consumption was found to be higher in rats with experimentally induced hyperthyroidism (from 20 to 60% depending on the experimental scheme used), with a slight decrease in the efficiency of oxidative phosphorylation and respiratory state ratio. It was shown for the first time that the level the respiratory complexes of the electron transport chain in hyperthyroid rats increased; however, the quantity of complexes III and V changed unreliably. The assay of respiratory chain enzymes revealed that the activities of complexes I, II, and citrate synthase increased, whereas the activities complexes II + III, III, IV decreased in liver mitochondria of the experimental animals. Alterations in the oxidative state in liver mitochondria were found: a 60% increase in the hydrogen peroxide production rate and a 45% increase in lipid peroxidation. The activities of superoxide dismutase and catalase in the liver of experimental rats were higher than in the control. At the same time, the activity of glutathione peroxidase did not change. The data obtained indicate that the known activation of metabolism and changes in the oxidative status in thyrotoxicosis are associated with variations in the respiratory chain functioning and the antioxidant enzymes of mitochondria.

Interdependence of oxidative/antioxidant system indicators and thyroid status under conditions of prolonged exposure to small doses of radiation

We have studied the interdependence of the intensity of oxidative processes/antioxidant level and the thyroid status parameters in a group of students aged 18–24 who lived for a long time in the territory of enhanced radioecological control (density of soil contamination by isotopes (137Cs 3.7 ∙ 104 – 18.5 ∙ 104 Bq/m2). We examined 50 people from relatively environmentally friendly areas (control group) and 50 people from IV radiation zone (experimental group). In the experimental group, there were no individuals with clinical manifestations of thyroid pathology. However, subgroups with signs of hyperthyroidism and hypothyroidism were identified. We evaluated the level of cortisol, thyrotrophic hormone (TSH), triiodothyronine (T3), thyroxine (T4), malonic dialdehyde (MDA), ceruloplasmin (CP), transferrin (Tf), sulfhydryl groups (SH); we calculated the oxidative stress index (OSI). The research was conducted one month before the examination time and also during the exams as a factor in increased emotional stress. A lowered CP level was found in the subgroup with signs of hypothyroidism; SH groups – in all subgroups, separated by thyroid status. The oxidative stress index was higher in all students examined of the experimental group, compared with the control. The growth of MDA level is marked in the experimental group – it is the most strongly pronounced in conditions of additional emotional load in people with signs of hyperthyroidism and hypothyroidism. CP level significantly decreased in the subgroup of hyperthyroidism on the background of T3 decrease. OSI increased in all students examined from the experimental group. In the subgroup of hypothyroidism it became significantly higher than in the subgroup of euthyroidism. A positive correlation between the levels of CP and T3 was found. The highest values of the correlation coefficients were noted for subgroups with signs of hyperthyroidism and hypothyroidism, with the coefficient significance increasing under conditions of emotional stress. The index of oxidative stress in the experimental group positively correlated with the level of TSH – in terms of emotional stress, the statistical significance of the coefficients disappeared. In the subgroups divided by thyroid status, variability of interactions between OSI and T3 was observed but it was not statistically significant. It was found that the participation of thyroid status in supporting redox homeostasis in people aged 18–24 who suffered from chronic small-doze radiation exposure was realized mainly by the influence on the antioxidant system. The ability of thyroid hormones to maintain a proper antioxidant state was suppressed in this group. The unbalanced relationship between thyroid hormones and oxidative stress indicators is strongly manifested under conditions of additional emotional stress.

Insulin resistance and diabetes in hyperthyroidism: a possible role for oxygen and nitrogen reactive species

In addition to insulin, glycemic control involves thyroid hormones. However, an excess of thyroid hormone can disturb the blood glucose equilibrium, leading to alterations of carbohydrate metabolism and, eventually, diabetes. Indeed, experimental and clinical hyperthyroidism is often accompanied by abnormal glucose tolerance. A common characteristic of hyperthyroidism and type 2 diabetes is the altered mitochondrial efficiency caused by the enhanced production of reactive oxygen and nitrogen species. It is known that an excess of thyroid hormone leads to increased oxidant production and mitochondrial oxidative damage. It can be hypothesised that these species represent the link between hyperthyroidism and development of insulin resistance and diabetes, even though direct evidence of this relationship is lacking. In this review, we examine the literature concerning the effects of insulin and thyroid hormones on glucose metabolism and discuss alterations of glucose metabolism in hyperthyroid conditions and the cellular and molecular mechanisms that may underline them.

Triiodothyronine attenuates the progression of renal injury in a rat model of chronic kidney disease

This study was designed to investigate whether and how triiodothyronine (T3) affects renal function in an experimental model of chronic kidney disease. Twenty-four female rats were divided into the following groups: sham-operated control group (n = 8), 5/6 nephrectomized group (Nx, n = 8), and 5/6 nephrectomized group treated with T3 for 2 weeks (T3-Nx, n = 8). T3 administration significantly decreased serum levels of urea, creatinine, tumour necrosis factorα, and interleukin-6 compared with serum levels in the Nx group. The levels of malondialdehyde, transforming growth factor β, fibronectin, and collagen IV, as well as the expression of inducible nitric oxide synthase, nuclear factor κB, poly(ADP-ribose) polymerase, caspase-3, and Bax were all significantly decreased, though not normalized, in the remnant kidney of rats in the T3-Nx group compared with Nx rats. Glutathione, heme oxygenase-1 levels, as well as endothelial nitric oxide synthase expression were increased in the remnant kidney of the T3-Nx group. Histological studies revealed focal necrosis of renal tubules associated with inflammatory cell infiltration and fibrosis in the Nx group. These changes were alleviated in T3-Nx rats. This study showed that T3 administration attenuated the clinical and histological signs of renal injury in 5/6 nephrectomized rats by mitigating renal oxidative stress, inflammation, apoptosis, and fibrosis.

Neonatal hypothyroidism affects testicular glucose homeostasis through increased oxidative stress in prepubertal mice: effects on GLUT3, GLUT8 and Cx43

Thyroid hormones (THs) play an important role in maintaining the link between metabolism and reproduction and the altered THs status is associated with induction of oxidative stress in various organs like brain, heart, liver and testis. Further, reactive oxygen species play a pivotal role in regulation of glucose homeostasis in several organs, and glucose utilization by Leydig cells is essential for testosterone biosynthesis and thus is largely dependent on glucose transporter 8 (GLUT8). Glucose uptake by Sertoli cells is mediated through glucose transporter 3 (GLUT3) under the influence of THs to meet energy requirement of developing germ cells. THs also modulate level of gap junctional protein such as connexin 43 (Cx43), a potential regulator of cell proliferation and apoptosis in the seminiferous epithelium. Although the role of transient neonatal hypothyroidism in adult testis in terms of testosterone production is well documented, the effect of THs deficiency in early developmental period and its role in testicular glucose homeostasis and oxidative stress with reference to Cx43 in immature mice remain unknown. Therefore, the present study was conducted to evaluate the effect of neonatal hypothyroidism on testicular glucose homeostasis and oxidative stress at postnatal days (PND) 21 and 28 in relation to GLUT3, GLUT8 and Cx43. Hypothyroidism induced by 6-propyl-2-thiouracil (PTU) markedly decreased testicular glucose level with considerable reduction in expression level of GLUT3 and GLUT8. Likewise, lactate dehydrogenase (LDH) activity and intratesticular concentration of lactate were also decreased in hypothyroid mice. There was also a rise in germ cell apoptosis with increased expression of caspase-3 in PTU-treated mice. Further, neonatal hypothyroidism affected germ cell proliferation with decreased expression of proliferating cell nuclear antigen (PCNA) and Cx43. In conclusion, our results suggest that neonatal hypothyroidism alters testicular glucose homeostasis via increased oxidative stress in prepubertal mice, thereby affecting germ cell survival and proliferation.

The Effect of Experimental Thyroid Dysfunction on Markers of Oxidative Stress in Rat Pancreas

Preclinical Research The aim of the present study was to evaluate the effects of thyroid dysfunction on markers of oxidative stress in rat pancreas. Hypothyroidism and hyperthyroidism were, respectively, induced in rats via administration of propylthiouracil (PTU) and L-thyroxine sodium salt in drinking water for 45 days. The activities of superoxide dismutase (SOD), catalase (CAT), glutathioen peroxidase (GPx), glutathione reductase (GR), glucose-6-phosphate dehydrogenase (G6PD), xanthine oxidase (XO), and nonenzymatic markers of oxidative stress including malondialdehyde (MDA), protein carbonyl (PC), reduced glutathione (GSH), and total thiols (T-SH) were determined in the rat pancreas. In hyperthyroid rats, pancreatic CAT, SOD, GPx, GR, XO, G6PD activities were increased compared with those in hypothyroid and control groups. There were no differences in activities of antioxidant enzymes between hypothyroid and control rats. Pancreatic MDA and PC in hyperthyroid rats increased compared with hypothyroid and the control animals. Whereas, hyperthyroid rats had decreased levels of tissue GSH and T-SH compared with hypothyroid and the control groups. The findings showed that only GSH level has decreased significantly in the hypothyroid group compared with control groups. In conclusion, our results showed that experimental hyperthyroidism induces oxidative stress in pancreas of rats, but hypothyroidism has no major impact on oxidative stress markers. Drug Dev Res 77 : 199-205, 2016.   © 2016 Wiley Periodicals, Inc.

Thyroid Hormones, Oxidative Stress, and Inflammation

Inflammation and oxidative stress (OS) are closely related processes, as well exemplified in obesity and cardiovascular diseases. OS is also related to hormonal derangement in a reciprocal way. Among the various hormonal influences that operate on the antioxidant balance, thyroid hormones play particularly important roles, since both hyperthyroidism and hypothyroidism have been shown to be associated with OS in animals and humans. In this context, the nonthyroidal illness syndrome (NTIS) that typically manifests as reduced conversion of thyroxine (T₄) to triiodothyronine (T₃) in different acute and chronic systemic conditions is still a debated topic. The pathophysiological mechanisms of this syndrome are reviewed, together with the roles of deiodinases, the enzymes responsible for the conversion of T₄ to T₃, in both physiological and pathological situations. The presence of OS indexes in NTIS supports the hypothesis that it represents a condition of hypothyroidism at the tissue level and not only an adaptive mechanism to diseases.

Role of Oxidative Stress in Thyroid Hormone-Induced Cardiomyocyte Hypertrophy and Associated Cardiac Dysfunction: An Undisclosed Story

Cardiac hypertrophy is the most documented cardiomyopathy following hyperthyroidism in experimental animals. Thyroid hormone-induced cardiac hypertrophy is described as a relative ventricular hypertrophy that encompasses the whole heart and is linked with contractile abnormalities in both right and left ventricles. The increase in oxidative stress that takes place in experimental hyperthyroidism proposes that reactive oxygen species are key players in the cardiomyopathy frequently reported in this endocrine disorder. The goal of this review is to shed light on the effects of thyroid hormones on the development of oxidative stress in the heart along with the subsequent cellular and molecular changes. In particular, we will review the role of thyroid hormone-induced oxidative stress in the development of cardiomyocyte hypertrophy and associated cardiac dysfunction, as well as the potential effectiveness of antioxidant treatments in attenuating these hyperthyroidism-induced abnormalities in experimental animal models.

Thyroid hormone in the frontier of cell protection, survival and functional recovery

Thyroid hormone (TH) exerts important actions on cellular energy metabolism, accelerating O2consumption with consequent reactive oxygen species (ROS) generation and redox signalling affording cell protection, a response that is contributed by redox-independent mechanisms. These processes underlie genomic and non-genomic pathways, which are integrated and exhibit hierarchical organisation. ROS production led to the activation of the redox-sensitive transcription factors nuclear factor-κB, signal transducer and activator of transcription 3, activating protein 1 and nuclear factor erythroid 2-related factor 2, promoting cell protection and survival by TH. These features involve enhancement in the homeostatic potential including antioxidant, antiapoptotic, antiinflammatory and cell proliferation responses, besides higher detoxification capabilities and energy supply through AMP-activated protein kinase upregulation. The above aspects constitute the molecular basis for TH-induced preconditioning of the liver that exerts protection against ischemia-reperfusion injury, a strategy also observed in extrahepatic organs of experimental animals and with other types of injury, which awaits application in the clinical setting. Noteworthy, re-adjusting TH to normal levels results in several beneficial effects; for example, it lengthens the cold storage time of organs for transplantation from brain-dead donors; allows a superior neurological outcome in infants of <28 weeks of gestation; reduces the cognitive side-effects of lithium and improves electroconvulsive therapy in patients with bipolar disorders.

Effects of thyroid hormones on the antioxidative status in the uterus of young adult rats

Thyroid hormones and oxidative stress play significant roles in the normal functioning of the female reproductive system. Nitric oxide (NO), a free radical synthesized by nitric oxide synthases (NOS), participates in the regulation of thyroid function and is also a good biomarker for assessment of the oxidative stress status. Therefore, the purpose of this study was to investigate effects of thyroid hormones on uterine antioxidative status in young adult rats. Thirty immature female Sprague-Dawley rats were randomly divided into three groups: control, hypothyroid (hypo-T) and hyperthyroid (hyper-T). The results showed the body weights decreased significantly in both the hypo-T and hyper-T groups and that uterine weights were decreased significantly in the hypo-T group. The serum concentrations of total triiodothyronine (T3) and thyroxine (T4), as well as estradiol (E2), were significantly decreased in the hypo-T group, but increased in the hyper-T group. The progesterone (P4) concentrations in the hypo- and hyperthyroid rats markedly decreased. Immunohistochemistry results provided evidence that thyroid hormone nuclear receptor α/β (TRα/β) and three NOS isoforms were located in different cell types of rat uteri. The NO content and total NOS and inducible NOS (iNOS) activities were markedly diminished in the hypo-T group but increased in the hyper-T group. Moreover, the activities of both glutathione peroxidase (GSH-Px) and catalase (CAT) exhibited significant decreases and increases in the hypo-T and hyper-T groups, respectively. The malondialdehyde (MDA) contents in both the hypo-T and hyper-T groups showed a significant increase. Total superoxide dismutase (T-SOD) activity in the hypo- and hyper-T rats markedly decreased. In conclusion, these results indicated that thyroid hormones have an important influence on the modulation of uterine antioxidative status.

Thyroid hormones and antioxidant systems: focus on oxidative stress in cardiovascular and pulmonary diseases

In previous works we demonstrated an inverse correlation between plasma Coenzyme Q₁₀ (CoQ₁₀) and thyroid hormones; in fact, CoQ₁₀ levels in hyperthyroid patients were found among the lowest detected in human diseases. On the contrary, CoQ₁₀ is elevated in hypothyroid subjects, also in subclinical conditions, suggesting the usefulness of this index in assessing metabolic status in thyroid disorders. A Low-T3 syndrome is a condition observed in several chronic diseases: it is considered an adaptation mechanism, where there is a reduction in pro-hormone T4 conversion. Low T3-Syndrome is not usually considered to be corrected with replacement therapy. We review the role of thyroid hormones in regulation of antioxidant systems, also presenting data on total antioxidant capacity and Coenzyme Q₁₀. Published studies suggest that oxidative stress could be involved in the clinical course of different heart diseases; our data could support the rationale of replacement therapy in low-T3 conditions.

Heme oxygenase-1 is induced by thyroid hormone and involved in thyroid hormone preconditioning-induced protection against renal warm ischemia in rat

Thyroid hormone pretreatment was indicated to increase tissue tolerance to ischemia-reperfusion injury (IRI) in various organs, but the underlying molecular mechanisms remains largely unknown. Induction of heme oxygenase-1 (HO-1) protects organs against IRI. The present study investigated the effect of thyroid hormone on HO-1 expression and the possible relation between HO-1 and the thyroid hormone induced renal protection. T(3) administration in rat kidneys induced HO-1 expression in a time-dependent and dose-dependent way, and its expression was accompanied with significant depletion of reduced glutathione and increase in malondialdehyde content, showing a moderate oxidative stress that turns to normal level 48 h after drug injection. Thyroid hormone pretreatment (10 μg/100g body weight) 48 h before IR procedure significantly decreased serum creatinine and urea nitrogen and preserved renal histology, with significant reduction of parameters about oxidative stress and over-expression of HO-1 compared with that of IR group. In conclusion, T(3) administration involving oxidative stress in kidney exerts significant enhancement of HO-1 expression which may, at least in part, account for the renal preconditioning induced by T(3).

Oxidative stress in cold-induced hyperthyroid state

Exposure of homeothermic animals to low environmental temperature is associated with oxidative stress in several body tissues. Because cold exposure induces a condition of functional hyperthyroidism, the observation that tissue oxidative stress also happens in experimental hyperthyroidism, induced by 3,5,3'-triiodothyronine (T(3)) treatment, suggests that this hormone is responsible for the oxidative damage found in tissues from cold-exposed animals. Examination of T(3)-responsive tissues, such as brown adipose tissue (BAT) and liver, shows that changes in factors favoring oxidative modifications are similar in experimental and functional hyperthyroidism. However, differences are also apparent, likely due to the action of physiological regulators, such as noradrenaline and thyroxine, whose levels are different in cold-exposed and T(3)-treated animals. To date, there is evidence that biochemical changes underlying the thermogenic response to cold as well as those leading to oxidative stress require a synergism between T(3)- and noradrenaline-generated signals. Conversely, available results suggest that thyroxine (T(4)) supplies a direct contribution to cold-induced BAT oxidative damage, but contributes to the liver response only as a T(3) precursor.

Hormetic responses of thyroid hormone calorigenesis in the liver: Association with oxidative stress

Thyroid hormone (L-3,3',5-triiodothyronine, T(3)) exerts calorigenic effects by accelerating mitochondrial O(2) consumption through transcriptional activation of respiratory genes, with consequent increased reactive oxygen species (ROS) production. In the liver, ROS generation occurs at different sites of hepatocytes and in the respiratory burst of Kupffer cells, triggering the activation of the transcription factors nuclear factor-kappaB, signal transducer and activator of transcription 3, and activating protein 1. Under these conditions, the redox upregulation of Kupffer cell-dependent expression of cytokines [tumor necrosis factor-alpha, interleukin (IL)-1, and IL-6] is achieved, which upon interaction with specific receptors in hepatocytes trigger the expression of antioxidant enzymes (manganese superoxide dismutase, inducible nitric oxide synthase), antiapoptotic proteins (Bcl-2), and acute-phase proteins (haptoglobin, beta-fibrinogen). These responses and the promotion of hepatocyte and Kupffer cell proliferation observed represent hormetic effects re-establishing redox homeostasis, promoting cell survival, and protecting the liver against ischemia-reperfusion (IR) injury. It is proposed that hormesis underlying T(3) action may constitute a novel preconditioning strategy for IR injury during liver surgery in man or in liver transplantation using reduced-size grafts from living donors, considering that (i) with the exception of the controversial ischemic preconditioning, all other studied strategies have failed to reach the clinical setting and (ii) T(3) is a well-tolerated therapeutic agent that either lacks major adverse effects or has minimal and controlled side effects.

Kupffer-cell activity is essential for thyroid hormone rat liver preconditioning

We studied the role of Kupffer cell functioning in T3 liver preconditioning against ischemia-reperfusion (IR) injury using the macrophage inactivator gadolinium chloride (GdCl3) previous to T3 treatment. Male Sprague-Dawley rats given a single i.p. dose of 0.1 mg T3/kg were subjected to 1 h ischemia followed by 20 h reperfusion, in groups of animals pretreated with 10 mg GdCl3/kg i.v. 72 h before T(3) or with the respective vehicles. IR resulted in significant enhancement of serum aspartate aminotransferase (3.3-fold increase) and tumor necrosis factor-alpha (93% increase) levels, development of liver damage, and diminished nuclear factor-kappaB DNA binding over control values. These changes, which were suppressed by the T3 administration prior to IR, persisted in animals given GdCl3 before T3 treatment, under conditions of complete elimination of ED2+ Kupffer cells achieved in a time window of 72 h. It is concluded that Kupffer cell functioning is essential for T3 liver preconditioning, assessed in a warm IR injury model by hepatic macrophage inactivation.

Hormones and antioxidant systems: role of pituitary and pituitary-dependent axes

Oxidative stress, a condition defined as unbalancing between production of free radicals and antioxidant defenses, is an important pathogenetic mechanism in different diseases. Despite the abundant literature, many aspects of hormone role in regulating antioxidant synthesis and activity still remain obscure. Therefore, we reviewed experimental data, in vivo and in vitro, about the effects of the different pituitary- dependent axes on antioxidant levels, trying to give a broad view from hormones which also have antioxidant properties to the classic antioxidants, from the lipophilic antioxidant Coenzyme Q10, strictly related to thyroid function, to total antioxidant capacity, a measure of non-protein non-enzymatic antioxidants in serum and other biological fluids. Taken together, these data underline the importance of oxidative stress in various pituitary-dependent disorders, suggesting a possible clinical usefulness of antioxidant molecules.

Oxidative stress signaling underlying liver disease and hepatoprotective mechanisms

Oxidative stress is a redox imbalance between pro-oxidants and antioxidants in favour of the former ones, leading to different responses depending on the level of pro-oxidants and the duration of the exposure. In this article, we discuss the damaging or cytoprotective signaling mechanisms associated with oxidative stress by addressing (1) the role of prolonged and severe oxidative stress and insulin resistance as determinant factors in the pathogenesis of non-alcoholic fatty liver disease associated with obesity, which, with the concurrence of nutritional factors, may determine the onset of fatty liver and its progression to steatohepatitis; and (2) the development of an acute and mild pro-oxidant state by thyroid hormone administration, which elicits the redox up-regulation of the expression of proteins affording cell protection, as a preconditioning strategy against ischemia-reperfusion liver injury.

The role of allopurinol on oxidative stress in experimental hyperthyroidism

AIM

During hyperthyroidism, production of free oxygen radicals derives, where xanthine oxidase may also play an important role. Allopurinol, a xanthine oxidase inhibitor, has a significant effect on thyrotoxicosis-related oxidative stress. However, the relationship between thyroid hormones, oxidative stress parameters and allopurinol remains to be explored.

METHODS

Forty-two Wistar albino rats were divided into three groups. Rats in group A served as negative controls, while group B had untreated thyrotoxicosis and group C received allopurinol. Hyperthyroidism was induced by daily 0.2 mg/kg L-thyroxine intraperitoneally in groups B and C; 40 mg/kg allopurinol were given daily intraperitoneally. Efficacy of the treatment was assessed after 72 h and 21 days, by measuring serum xanthine oxidase (XO), malondialdehyde (MDA), glutathione (GSH), glutathione reductase (GR), glutathione peroxidase (GPx) and nitric oxide derivates (NO*x).

RESULTS

In both time periods, serum XO, MDA, GSH and NO*x levels were significantly increased after thyroid hormone induction (p<0.05). Levels of XO, MDA and NO*x decreased with allopurinol treatment (p<0.05). There was a remarkable decrease in triiodothyronine levels in group C after 72 h (p<0.05), and in both triiodothyronine and thyroxine levels in group C after 21 days (p<0.05). There was no difference between groups B and C in means of serum GSH, GR and GPx levels (p>0.05).

CONCLUSIONS

This study suggests an association between allopurinol and the biosynthesis of thyroid hormones. Allopurinol prevents the hyperthyroid state, which is mediated predominantly by triiodothyronine and not by XO. This issue has to be questioned in further studies where allopurinol is administered in control subjects.

The role of thyroid hormone in testicular development and function

Thyroid hormone is a critical regulator of growth, development, and metabolism in virtually all tissues, and altered thyroid status affects many organs and systems. Although for many years testis has been regarded as a thyroid hormone unresponsive organ, it is now evident that thyroid hormone plays an important role in testicular development and function. A considerable amount of data show that thyroid hormone influences steroidogenesis as well as spermatogenesis. The involvement of tri-iodothyronine (T(3)) in the control of Sertoli cell proliferation and functional maturation is widely accepted, as well as its role in postnatal Leydig cell differentiation and steroidogenesis. The presence of thyroid hormone receptors in testicular cells throughout development and in adulthood implies that T(3) may act directly on these cells to bring about its effects. Several recent studies have employed different methodologies and techniques in an attempt to understand the mechanisms underlying thyroid hormone effects on testicular cells. The current review aims at presenting an updated picture of the recent advances made regarding the role of thyroid hormones in male gonadal function.

Hyperthyroidism in the developing rat testis is associated with oxidative stress and hyperphosphorylated vimentin accumulation

Hyperthyroidism was induced in rats and somatic indices and metabolic parameters were analyzed in testis. In addition, the morphological analysis evidenced testes maturation and intense protein synthesis and processing, supporting the enhancement in vimentin synthesis in hyperthyroid testis. Furthermore, vimentin phosphorylation was increased, indicating an accumulation of phosphorylated vimentin associated to the cytoskeleton, which could be a consequence of the extracellular-regulated kinase (ERK) activation regulating the cytoskeleton. Biomarkers of oxidative stress demonstrated an increased basal metabolic rate measured by tissue oxygen consumption, as well as, increased TBARS levels. In addition, the enzymatic and non-enzymatic antioxidant defences appeared to respond according to the augmented oxygen consumption. We observed decreased total glutathione levels, with enhancement of reduced glutathione, whereas most of the antioxidant enzyme activities were induced. Otherwise, superoxide dismutase activity was inhibited. These results support the idea that an increase in mitochondrial ROS generation, underlying cellular oxidative damage, is a side effect of hyperthyroid-induced biochemical changes by which rat testis increase their metabolic capacity.

Thyroid hormone-induced oxidative stress in rodents and humans: a comparative view and relation to redox regulation of gene expression

Thyroid hormone (3,3',5-triiodothyronine, T(3)) exerts significant actions on energy metabolism, with mitochondria being the major target for its calorigenic effects. Acceleration of O(2) consumption by T(3) leads to an enhanced generation of reactive oxygen and nitrogen species in target tissues, with a higher consumption of cellular antioxidants and inactivation of antioxidant enzymes, thus inducing oxidative stress. This redox imbalance occurring in rodent liver and extrahepatic tissues with a calorigenic response, as well as in hyperthyroid patients, is further enhanced by an increased respiratory burst activity in Kupffer cells, which may activate redox-sensitive transcription factors such as NF-kappaB thus up-regulating gene expression. T(3) elicits an 80-fold increase in the serum levels of tumor necrosis factor-alpha (TNF-alpha), which is abolished by pretreatment with the antioxidants alpha-tocopherol and N-acetylcysteine, the Kupffer-cell inactivator GdCl(3), or an antisense oligonucleotide against TNF-alpha. In addition, T(3) treatment activates hepatic NF-kappaB, a response that is (i) inhibited by antioxidants and GdCl(3) and (ii) accompanied by induced mRNA expression of the NF-kappaB-responsive genes for TNF-alpha and interleukin (IL)-10. T(3) also increases the hepatic levels of mRNA for IL-1alpha and those of IL-1alpha in serum. Up-regulation of liver iNOS expression is also achieved by T(3), through a cascade initiated by TNF-alpha and involving IkappaB-alpha phosphorylation and NF-kappaB activation. In conclusion, T(3)-induced oxidative stress in the liver enhances the DNA-binding of NF-kappaB and the NF-kappaB-dependent expression of cytokines and iNOS by actions primarily exerted at the Kupffer cell level.

Effects of triiodothyronine-induced hyperthyroidism on lipid peroxidation, erythrocyte resistance and iron-binding and iron-oxidizing antioxidant properties of plasma in the rabbit

The effect of hyperthyroidism on some oxidative stress parameters is reported. The hyperthyroid state was induced by intraperitoneal injection of triiodothyronine (T3)(10 microg/kg body weight) for 14 days in two groups of female rabbits (3 and 12 months old). The T3 injection caused increase by 1.5-fold to 1.7-fold in T3 serum level, and 2-fold to 3-fold decrease (age-dependent) in body weight gain at the end of experimental period. The induced hyperthyroidism caused a significant increase in the serum concentration of the lipid peroxidation end-product malondialdehyde and lowered erythrocyte resistance to oxidative stress when subjected to the free radical generator 2,2'-azobis(2-amidinopropane) hydrochloride in vitro. The half maximum haemolysis time (HT50) decreased in the both experimental groups of rabbits, by about 12 min in the 3-month-old animals and 27 min in the 12-month-old animals. The study showed for the first time that hyperthyroidism enhances the ability of plasma to protect against iron-binding and iron oxidizing organic radicals. The scavenging property and antioxidant capacity of plasma against iron-binding inorganic radicals also increased. Measurement of erythrocyte resistance to oxidative stress and the protective ability of plasma against oxygen radicals discriminates the thyroid hormone modulatory effects in defence mechanisms against lipid peroxidation.

Cardiac and renal antioxidant enzymes and effects of tempol in hyperthyroid rats

This study evaluated the activity of cardiac and renal antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), and glutathione reductase (GR)] and whether chronic treatment with tempol, a cell membrane-permeable SOD mimetic, ameliorates the hypertension of hyperthyroidism. Two experiments were performed. In experiment I, the following four groups of male Wistar rats were used: control group and three groups that received thyroxine (T4) at 10, 50, or 75 microg x rat(-1) x day(-1). In experiment II, tempol was orally administered (18 mg x kg(-1) x day(-1)) to control and T4-treated (75 microg x rat(-1) x day(-1)) rats. All treatments were maintained for 6 wk. Body weight, tail systolic blood pressure (BP), and heart rate were measured one time a week, and direct BP and morphological, metabolic, plasma, and renal variables were measured at the end of the experiment. Enzymatic activities were measured in renal cortex and medulla and right and left ventricles. In renal cortex, SOD activity was decreased in the T4-75 group, and there was a dose-related increase in CAT activity and decrease in GPX and GR activities in T4-treated groups. Activity of all antioxidant enzymes was reduced in left ventricle in T4-50 and T4-75 groups and in right ventricle in the T4-75 group. Tempol reduced BP, plasma malondialdehyde, and total urinary excretion of F2 isoprostanes in hypertensive hyperthyroid rats but not in controls. Tempol did not improve cardiac hypertrophy, proteinuria, or creatinine clearance in hyperthyroid rats. In conclusion, the results obtained indicate that the activity of SOD, GPX, and GR in renal and cardiac tissues is decreased in hyperthyroidism and that antioxidant treatment with tempol ameliorates T4-induced hypertension.

Elevated urinary 8-isoprostaglandin F(2alpha) in females with Graves' hyperthyroidism

In this study, we investigate how oxidative stress alters the urinary F2-isoprostanes' level and we examine the correlation between 8-isoPGF(2alpha) and thyroid hormones in female patients with Graves' hyperthyroidism. We quantitatively determined the concentrations of urinary F2-isoprostanes using gas chromatography-mass spectrometry in the selected ion-monitoring mode. We recruited individuals in the following three groups of subjects for this study: (1) female hyperthyroidism patients (n = 14, 21-71 years), (2) female hypothyroidism patients (n = 16, 16-66 years), and (3) female age-matched normal controls (n = 10, 20-61 years). The average concentration of 8-iso prostaglandin F(2alpha) (8-isoPGF(2alpha)) in hyperthyroidism patients was significantly higher than that in the healthy controls (P < 0.05). The concentration of 8-isoPGF(2alpha) in hypothyroidism patients was similar to that in normal controls. Although the level of 8-isoPGF(2alpha) in two of the patients was slightly elevated, the P value was not significant (NS). Our data suggest that the increased level of urinary 8-isoPGF(2alpha) may reflect possible oxidation injuries in hyperthyroidism patients due to the high level of thyroid hormones. Therefore, the elevated 8-isoPGF(2alpha) in patients could be used as an important biomarker for hyperthyroidism disease.

Thyroid hormone-induced oxidative stress triggers nuclear factor-kappaB activation and cytokine gene expression in rat liver

Nuclear factor-kappaB (NF-kappaB) is a redox-sensitive factor responsible for the transcriptional activation of cytokine-encoding genes. In this study, we show that 3,3,5-triiodothyronine (T(3)) administration to rats activates hepatic NF-kappaB, as assessed by electrophoretic mobility shift assay. This response coincides with the onset of calorigenesis and enhancement in hepatic respiration, and is suppressed by the antioxidants alpha-tocopherol and N-acetylcysteine or by the Kupffer cell inactivator gadolinium chloride. Livers from hyperthyroid rats with enhanced NF-kappaB DNA-binding activity show induced mRNA expression of the NF-kappaB-responsive genes for tumor necrosis factor-alpha (TNF-alpha) and interleukin- (IL-) 10, as evidenced by reverse transcription-polymerase chain reaction assay, which is correlated with increases in the serum levels of the cytokines. T(3) also increased the hepatic levels of mRNA for IL-1alpha and those of IL-1alpha in serum, with a time profile closely related to that of TNF-alpha. It is concluded that T(3)-induced oxidative stress enhances the DNA-binding activity of NF-kappaB and the NF-kappaB-dependent expression of TNF-alpha and IL-10 genes.

Influence of hypothyroidism on lipid peroxidation, erythrocyte resistance and antioxidant plasma properties in rabbits

The effect of hypothyroidism on some oxidative stress parameters is reported. Moderate hypothyroid state was induced in two groups of female rabbits (3 and 12 months old) by giving 50 mg/kg body weight (BW) of propylthiouracil (PTU) per os for 6 days and 20 mg/kg BW of methimazole (MMI) for further 14 days. Serum T4 and T3 concentrations decreased by about 38-40 and 32-36%, respectively. The induced hypothyroidism resulted in a significant decrease in the serum concentration of the lipid peroxidation end-product malondialdehyde, as measured by the thiobarbituric-acid assay. Erythrocytes of hypothyroid animals exhibited higher resistance to oxidative stress, while submitted to free radicals generator 2,2'-azo-bis(2-amidinopropane) hydrochloride (AAPH) in vitro. Using two detector systems (phospholipid liposomes and deoxyribose), sensitive to either organic or inorganic oxygen radical damage, the ability of euthyroid and hypothyroid rabbit plasma to protect against oxygen radicals was evaluated. The plasma of hypothyroid animals showed about 20% higher ability to protect against iron-binding organic radicals, but about 50% lower chain-breaking antioxidant activity. The antioxidant capacity of plasma against inorganic radicals was not affected by hypothyroidism. In conclusion, the results show that thyroid hormones modulate the free-radical-induced oxidative damage of lipids and that hypothyroidism offers some protection against lipid peroxidation.

Thyroid hormone-induced oxidative damage on lipids, glutathione and DNA in the mouse heart

Oxygen radicals of mitochondrial origin are involved in oxidative damage. In order to analyze the possible relationship between metabolic rate, oxidative stress and oxidative damage, OF1 female mice were rendered hyper- and hypothyroid by chronic administration of 0.0012% L-thyroxine (T4) and 0.05% 6-n-propyl-2-thiouracil (PTU), respectively, in their drinking water for 5 weeks. Hyperthyroidism significantly increased the sensitivity to lipid peroxidation in the heart, although the endogenous levels of lipid peroxidation were not altered. Thyroid hormone-induced oxidative stress also resulted in higher levels of GSSG and GSSG/GSH ratio. Oxidative damage to mitochondrial DNA was greater than that to genomic DNA. Hyperthyroidism decreased oxidative damage to genomic DNA. Hypothyroidism did not modify oxidative damage in the lipid fraction but significantly decreased GSSG and GSSG/GSH ratio and oxidative damage to mitochondrial DNA. These results indicate that thyroid hormones modulate oxidative damage to lipids and DNA, and cellular redox potential in the mouse heart. A higher oxidative stress in the hyperthyroid group is presumably neutralized in the case of nuclear DNA by an increase in repair activity, thus protecting this key molecule. Treatment with PTU, a thyroid hormone inhibitor, reduced oxidative damage in the different cell compartments.

Iron-induced changes in nitric oxide and superoxide radical generation in rat liver after lindane or thyroid hormone treatment

The involvement of cytosolic nitric oxide (NO) and mitochondrial superoxide radical (O2(.-)) production was evaluated as a mechanism triggering liver oxidative stress in lindane (40 mg/kg) or L-3,3',5-triiodothyronine (T3, 0.1 mg/kg for 2 consecutive days) treated animals (male Sprague-Dawley rats) subjected to iron overload (200 mg/kg). Lindane and iron led to 504 and 210% increases in the content of hepatic protein carbonyls as an index of oxidative stress, with a 706% enhancement being produced by their combined administration. T3 did not alter this parameter, whereas iron overload increased the content of protein carbonyls by 116% in hyperthyroid rats. Lindane increased NO generation by 106% without changes in generation of O2(.-), whereas iron enhanced both parameters by 109 and 80% over control values, respectively, with a net 33 and 46% decrease, respectively, being elicited by the combined treatment related to iron overload alone. Hyperthyroidism increased liver NO (69%) and O2(.-) (110%) generation compared to controls, effects that were either synergistically augmented or suppressed by iron overload, respectively. The in vitro addition of iron (1 micromol/mg protein) to liver cytosolic fractions from euthyroid (97%) and hyperthyroid (173%) rats also enhanced NO generation. The effects of iron overload on mitochondrial O2(.-) production by hyperthyroid rats were reproduced by the in vitro addition of 1 micromol iron/mg protein and abolished by the in vivo pretreatment with the iron chelator desferrioxamine (500 mg/kg). It is concluded that liver oxidative stress induced by iron overload is independent of NO and O2(.-) production in lindane-treated rats, whereas in hyperthyroid animals NO generation is a major factor contributing to this redox imbalance.